I found an interesting collection of articles while I was looking for more information about Hieronymous. Here, http://www.english.illinois.edu/maps/poets/a_f/eliot/eliot.htm .

It made a lot of interesting points, what most interested me what the notion of being fruitful in the poetry. Of course on first glance, The Wasteland is overwhleming. You ask yourself, hoow could this even be narrowed to a point, what could Elliot possibly be getting at? That question has lingered since I first read it, and I'm happy to say this Hieronymous snag has brought me to a new level of understanding. 

The play that he references in the final stanza

 These fragments I have shored against my ruins
Why then Ile fit you. Hieronymo’s mad againe.

 See, Hieronymo was commisioned to design a play, and it was this that he used to exact revenge for his dead son. We have here a familiar theme, a play within a play, this is the protoype, or rather probably just a prototype of the play Hamlet. 
This theme that Elliot is picking up is the most real theme. By which I mean, it is one of the few themes of the human experience that all people share. The play is our culture our history, all of the events that have lead to our lives. The play within this play is what we do with it.
The reason that Elliot chose Hieronymo to reference instead of Hamlet is hard to put a finger on. I would say that the key difference is that Hamlet is Avenging is father, whereas Hieronymo is avenging his dead son. I think Elliot is warning us against a desolate point of view wherein we think the future is already lost based on the fact that history is bleak at best. Because while we are reacting to the tragedy of the play outside of our own play, that tragedy is the only thing we have. The cycle of death and rebirth is depressing, true, but it's all we've got.